User equipment and signal transmission method

ABSTRACT

A user equipment including: a selection unit that selects, based on a result of sensing performed in a first time window and on a transmission interval of a signal, one or more resource candidates in a second time window after the first time window; and a transmission unit that selects a resource for transmitting a signal from the selected one or more resource candidates, and transmits the signal.

TECHNICAL FIELD

The present invention relates to a user equipment and a signaltransmission method.

BACKGROUND ART

A device to device (D2D) technology, in which user equipments perform adirect communication without through a radio base station, has beenexamined in long term evolution (LTE) and a succession system (forexample, LTE-Advanced (LET-A), 4G, future radio access (FRA), 5G, andthe like) of the LTE (for example, Non-Patent Document 1).

The D2D can reduce congestion between a user equipment and a basestation, or can realize a communication between user equipments even ina case where the base station enters a communication impossible state atthe time of disaster and the like.

The D2D is largely classified into a D2D discovery that discoversanother user equipment that can establish a communication, and a D2Dcommunication (also referred to as “D2D direct communication” and“terminal-to-terminal direct communication”) in which a directcommunication is performed between user equipments. In the followingdescription, when not being particularly distinguished, the D2Dcommunication, the D2D discovery, and the like are simply referred to as“D2D”. In addition, a signal that is transmitted and received with theD2D is referred to as “D2D signal”.

In addition, in a 3rd generation partnership project (3GPP), realizationof V2X through extension of a D2D function has been examined. Here, theV2X is a part of intelligent transport systems (ITS), and is a generalterm of a vehicle to vehicle (V2V) that represents a communication typeperformed between vehicles, a vehicle to infrastructure (V2I) thatrepresents a communication type performed between a vehicle and aroad-side unit (RSU) that is provided on a roadside, a vehicle tonomadic device (V2N) that represents a communication type performedbetween a vehicle and a mobile terminal of a driver, and a vehicle topedestrian (V2P) that represents a communication type performed betweena vehicle and a mobile terminal of a pedestrian as illustrated in FIG.1.

CITATION LIST Non-patent Document

Non-Patent Document 1: “Key drivers for LTE success: ServicesEvolution”, September 2011, 3GPP, internet URL:http://www.3gpp.org/ftp/Information/presentations/presentations_2011/2011_09 LTE Asia/2011_LTE-Asia_3GPP Service evolution.pdf

Non-Patent Document 2: 3GPP TS 36.300 V13.2.0 (2015-12)

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

The V2X technology is based on the D2D technology defined in LTE. In theD2D technology, a mode in which a user equipment selects a resource withwhich a D2D signal is transmitted is largely classified into a mode inwhich the resource is dynamically allocated from a base station, and amode in which the user equipment autonomously selects the resource. Inthe V2X, particularly, in the V2V, the user equipment (for example, avehicle) exists in a high density, and moves at a high speed, and thusthe mode in which the resource is dynamically allocated is notefficient. Accordingly, it is assumed that the mode in which the userequipment autonomously selects the resource is used. In addition, in theV2X, it is also assumed that the user equipment reserves a futuretransmission resource and transmits the D2D signal by using the reservedresource so as to realize periodic data transmission.

Here, when a plurality of user equipments autonomously select (includingreselection) a transmission resource, if each of the user equipmentsfreely selects and reserves the resource, collision of resources occurs,and thus a user equipment on a reception side cannot appropriatelyreceive a signal. Here, in 3GPP, a sensing-based resource selectionmode, in which sensing of a resource is performed, and selection of aresource that is not used or reserved (may be referred to as“occupied”), is proposed.

Here, particularly, in the V2V, for example, it is assumed that data istransmitted in a period such as an interval of 100 ms and an interval of500 ms. Accordingly, when selecting a resource on the basis of a sensingresult, it is preferable that the user equipment selects a resource inconsideration of a data transmission interval that is desired. However,in the sensing-based resource selection mode that is proposed in current3GPP, a transmission interval of a signal that is transmitted is notconsidered. That is, in the current resource selection mode, first datatransmission can be performed with a resource that is selected, but insecond or later data transmission, there is a problem that resources maycollide with each other.

A technology that is disclosed has been made in consideration of theabove-described circumstances, and an object thereof is to provide atechnology capable of suppressing signal collision in a mode ofselecting a resource for signal transmission on the basis of a sensingresult.

Means for Solving Problem

According to a technology that is disclosed, there is provided a userequipment including:

a selection unit that selects, based on a result of sensing performed ina first time window and on a transmission interval of a signal, one ormore resource candidates in a second time window after the first timewindow; and

a transmission unit that selects a resource for transmitting a signalfrom the selected one or more resource candidates, and transmits thesignal.

EFfect of the Invention

According to the technology that is disclosed, it is possible to providea technology capable of suppressing signal collision in a mode ofselecting a resource for signal transmission on the basis of a sensingresult.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating a V2X;

FIG. 2A is a view illustrating a D2D;

FIG. 2B is a view illustrating a D2D;

FIG. 3 is a view illustrating a MAC PDU that is used in a D2Dcommunication;

FIG. 4 is a view illustrating a format of an SL-SCH subheader;

FIG. 5 is a view illustrating an example of a channel structure that isused in the D2D;

FIG. 6A is a view illustrating a structure example of a PSDCH;

FIG. 6B is a view illustrating a structure example of a PSDCH;

FIG. 7A is a view illustrating a structure example of a PSCCH and aPSSCH;

FIG. 7B is a view illustrating a structure example of a PSCCH and aPSSCH;

FIG. 8A is a view illustrating a resource pool configuration;

FIG. 8B is a view illustrating a resource pool configuration;

FIG. 9 is a view illustrating a configuration example of a radiocommunication system according to an embodiment;

FIG. 10 is a view illustrating a sensing-based resource selection mode;

FIG. 11 is a view illustrating a specific example of the resourceselection mode (Mode 1-1 thereof);

FIG. 12 is a view illustrating a specific example of the resourceselection mode (Mode 1-1 thereof);

FIG. 13 is a view illustrating a specific example of the resourceselection mode (Mode 1-2 thereof);

FIG. 14 is a view illustrating a specific example of the resourceselection mode (Mode 1-2 thereof);

FIG. 15 is a flowchart illustrating the resource selection mode (Mode 2thereof);

FIG. 16 is a view illustrating a specific example of the resourceselection mode (Mode 2 thereof);

FIG. 17 is a view illustrating a specific example of the resourceselection mode (Mode 2 thereof);

FIG. 18 is a view illustrating an example of a functional configurationof a user equipment according to the embodiment;

FIG. 19 is a view illustrating an example of a functional configurationof a base station according to the embodiment; and

FIG. 20 is a view illustrating an example of a hardware configuration ofthe base station and the user equipment according to the embodiment.

MODE(S) FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the invention will be described withreference to the accompanying drawings. Furthermore, the followingembodiment is illustrative only, and an embodiment to which theinvention is applied is not limited to the following embodiment. Forexample, in a radio communication system according to this embodiment, asystem of a mode in conformity to LTE is assumed, but the invention isapplicable to other modes without limitation to the LTE. Furthermore, inthis specification and claims, “LTE” is used in broad meaning includingnot only a communication mode corresponding to Release 8 or 9 of 3GPPbut also a fifth generation communication mode corresponding to Releasesubsequent to Release 10, 11, 12, 13, or 14 of the 3GPP.

In addition, description of this embodiment is mainly given of a V2X,but the technology according to this embodiment is also widelyapplicable to the whole D2D without limitation to the V2X. In addition,meaning of the “D2D” includes the V2X. In addition, a term of the “D2D”represents the whole inter-terminal communications without limitation tothe D2D in LTE.

In addition, the “D2D” is used in broad meaning including a procedure oftransmitting and receiving a D2D signal between user equipments UE, aprocedure of receiving (monitoring) the D2D signal by a base station,and a procedure of transmitting an uplink signal to a base station eNBby each of the user equipments UE in a case of RRC idle or in a casewhere connection with the base station eNB is not established.

<Overview of D2D>

First, description will be given of an overview of the D2D defined inLTE. Furthermore, the technology of the D2D to be described here can beused even in the V2X, and the user equipment UE in the embodiment of theinvention can execute transmission and reception of the D2D signalaccording to the technology.

As described above, the D2D is largely classified into “D2D discovery”and “D2D communication”. With regard to the “D2D discovery”, asillustrated in FIG. 2A, a resource pool for a discovery message issecured for each discovery period (also referred to as physical sidelinkdiscovery channel (PSDCH) period), and the user equipment UE transmits adiscovery message (discovery signal) in the resource pool. Detailedexamples include Type 1 and Type 2B. In Type 1, the user equipment UEautonomously selects a transmission resource in a resource pool. In Type2b, a quasi-static resource can be allocated through higher layersignaling (for example, an RRC signal).

With regard to the “D2D communication”, as illustrated in FIG. 2B, aresource pool for sidelink control information (SCI)/data transmissionis periodically secured. A transmission-side user equipment UE notifiesa reception side of a resource for data transmission and the like byusing an SCI with a resource that is selected in a control resource pool(physical sidelink control channel (PSCCH) resource pool), and transmitsdata with a resource for data transmission. More specific examples ofthe “D2D communication” include Mode 1 and Mode 2. In the Mode 1, aresource can be dynamically allocated with (enhanced) physical downlinkcontrol channel (E)PDCCH that is transmitted to a user equipment UE froma base station eNB. In Mode 2, the user equipment UE autonomouslyselects a transmission resource from a resource pool. As the resourcepool, a resource pool, which is notified with a system information block(SIB) or which is defined in advance, is used.

In LTE, a channel that is used in the “D2D discovery” is referred to asa PSDCH, a channel with which control information such as the SCI istransmitted in the “D2D communication” is referred to as a PSCCH, and achannel with which data is transmitted is referred to as a physicalsidelink shared channel (PSCCH).

As illustrated in FIG. 3, a medium access control (MAC) protocol dataunit (PDU) that is used in a communication of the D2D is constituted byat least a MAC header, a MAC control element, a MAC service data unit(SDU), and a padding. The MAC PDU may include other pieces ofinformation. The MAC header is constituted by one sidelink sharedchannel (SL-SCH) subheader, and one or more MAC PDU suheaders.

As illustrated in FIG. 4, the SL-SCH subheader is constituted by a MACPDU format version (V), transmission source information (SRC),transmission destination information (DST), a reserved bit (R), and thelike. V represents a MAC PDU format version that is allocated to aleading portion of the SL-SCH subheader and is used by a user equipmentUE. Information related to a transmission source is set in thetransmission source information. An identifier related to a ProSe UE IDmay also be set in the transmission source information. Informationrelated to a transmission destination is set in the transmissiondestination information. Information related to a ProSe Layer-2 Group IDmay also be set in the transmission destination information.

An example of a channel structure of the D2D is illustrated in FIG. 5.As illustrated in FIG. 5, a PSCCH resource pool and a PSSCH resourcepool which are used in the “D2D communication” are allocated. Inaddition, a PSDCH resource pool that is used in the “D2D discovery” isallocated in a period that is longer than a period of a channel of the“D2D communication”.

In addition, as a synchronization signal for the D2D, a primary sidelinksynchronization signal (PSSS) and a secondary sidelink synchronizationsignal (SSSS) are used. In addition, for example, a physical sidelinkbroadcast channel (PSBCH), which is used to transmit notificationinformation (broadcast information) such as a system band of the D2D, aframe number, and resource configuration information, is used for anoperation other than coverage.

FIG. 6A illustrates an example of the PSDCH resource pool that is usedin the “D2D discover”. The resource pool is set with a bitmap of asubframe, and thus the resource pool becomes a resource pool with animage as illustrated in FIG. 6A. This is also true of resource pools ofother channels. In addition, in the PSDCH, repetitive transmission(repetition) is performed while performing frequency hopping. The numberof repetition times can be set to, for example, 0 to 3. In addition, asillustrated in FIG. 6B, the PSDCH has a PUSCH-based structure, and has astructure in which a demodulation reference signal (DM-RS) is inserted.

FIG. 7A illustrates an example of the PSCCH resource pool and the PSSCHresource pool which are used in the “D2D communication”. As illustratedin FIG. 7A, in the PSCCH, repetitive transmission (repetition) isperformed once while performing the frequency hopping. In the PSSCH,repetitive transmission (repetition) is performed three times whileperforming the frequency hopping. In addition, as illustrated in FIG.7B, the PSCCH and the PSSCH have a PUSCH-based structure, and has astructure in which the DM-RS is inserted.

FIGS. 8A and 8B illustrate an example of a resource pool configurationin the PSCCH, the PSDCH, and the PSSCH (Mode 2). As illustrated in FIG.8A, in a time direction, a resource pool is expressed as a subframebitmap. Furthermore, the bitmap is repeated by the number of times ofnum.reprtition. In addition, an offset, which indicates an initiationposition in each period, is designated.

In a frequency direction, contiguous allocation and non-contiguousallocation can be performed. FIG. 8B illustrates an example of thenon-contiguous allocation. As illustrated in the drawing, an initiationPRB, a termination PRB, and the number of PRBs (numPRB) are designated.

<System Configuration>

FIG. 9 is a view illustrating a configuration example of the radiocommunication system according to the embodiment. As illustrated in FIG.9, the radio communication system according to this embodiment includesa base station eNB, a user equipment UE1, and a user equipment UE2. InFIG. 9, the user equipment UE1 is intended as a transmission side, andthe user equipment UE2 is intended as a reception side. However, both ofthe user equipment UE1 and the user equipment UE2 include a transmissionfunction and a reception function. Hereinafter, when not beingparticularly discriminated, the user equipment UE1 and the userequipment UE2 are simply described as “user equipment UE”.

Each of the user equipment UE1 and the user equipment UE2 in FIG. 9 hasa cellular communication function as a user equipment UE in LTE, and aD2D function including signal transmission and reception with theabove-described channel. Furthermore, the user equipment UE1 and theuser equipment UE2 have a function of executing an operation that isdescribed in this embodiment. Furthermore, with regard to the cellularcommunication function and the existing D2D function, only partialfunctions (in a range capable of executing the operation described inthis embodiment) or the entirety of the functions may be provided.

In addition, the user equipment UE may be any device having the D2Dfunction, and examples thereof include a vehicle, a terminal of apedestrian, an RSU (a UE type RSU having a UE function), and the like.

In addition, the base station eNB has the cellular communicationfunction as the base station eNB in LTE, a function (setting informationnotification function and the like) capable of realizing a communicationof the user equipment UE in this embodiment. In addition, the basestation eNB includes an RSU (eNB type RSU having an eNB function).

In the following description, for example, “sensing” is performed by amethod of using a measurement result of reception power (may be referredto as reception energy or reception intensity), a method of using adecoding result of D2D control information (that i, a method in whichthe D2D control information transmitted from another user equipment UEis received and is decoded to sense a resource position that is reservedby the other user equipment UE), a combination of these methods, and thelike. In addition, the “resource” includes a time resource (for example,a subframe), or a time and frequency resource unless otherwise stated.In addition, description will be given on the assumption that the “D2Dsignal” may be a signal of the D2D communication (which may be D2Dcontrol information, data, or a combination of the D2D controlinformation and the data), but the “D2D” signal may be a message(discovery signal) of the D2D discovery without limitation thereto.

The user equipment UE according to this embodiment selects a resource,with which the D2D signal is transmitted, by using the followingsensing-based resource selection mode, and transmits the D2D signal withthe resource that is selected at a transmission interval that is desiredby the user equipment UE. Note that, the user equipment UE may includereservation information indicating that a resource for transmission of aD2D signal after the subsequent transmission interval is reserved in D2Dcontrol information transmitted with the resource that is selected so asto allow another user equipment UE to grasp the resource which isreserved by the user equipment UE.

<With Respect to Resource Selection Mode that is Studied in 3GPP>

Here, description will be given of a resource selection mode that issuggested in current 3GPP. The resource selection mode that is suggestedin 3GPP is realized by the following sequence of three steps to bedescribed below.

STEP 1: The entirety of resources (for example, a D2D resource pool),with which the D2D signal can be transmitted, are regarded as capable ofbeing used (not being reserved).

STEP 2: Among the resources which are regarded as capable of being usedin STEP 1, a reserved resource, which is grasped by decoding D2D controlinformation transmitted from another user equipment UE, is excluded.Alternatively, among the resources which are regarded as capable ofbeing used in STEP 1, a reserved resource, which is grasped by decodingD2D control information transmitted from another user equipment UE andsatisfies a predetermined condition, is excluded. Examples of thepredetermined condition include a case where power of demodulationreference signal (DM-RS) that is mapped to a data resource (for example,a resource of a PSSCH) indicated by the D2D control information is equalto or greater than a predetermined threshold value, or a case wherepower, which is estimated by a result obtained through measurement of aresource of the D2D control information, of data resource indicated bythe D2D control information is equal to or greater than a predeterminedthreshold value, and the like.

STEP 3: Reception power of the entirety (or a part that is determined inadvance (for example, resources with which a PSSCH can be transmitted,the same shall apply hereinafter) of resources (for example, a D2Dresource pool) in which the D2D signal can be transmitted is measured, apartial resource (for example, a resource of which reception power isequal to or greater than a predetermined threshold value) based on ameasurement result is further excluded from the remaining resourcesafter the exclusion in STEP 2 to select a subset of resources whichbecome the final resource selection candidate. That is, in the subset ofthe resources which become the final resource selection candidate, aresource, which is not an object to be excluded in STEP 2 and is not anobject to be excluded in STEP 3, remains. Subsequently, the userequipment UE randomly selects one resource that is actually used in datatransmission among the subset of the resources which become the finalresource selection candidate.

Note that, it may be considered that in STEP 3, the one resource that isused in data transmission is directly selected from the resources whichare not excluded in STEP 2. However, it is also assumed that the userequipment UE fails in decoding of the D2D control signal, and thus it issuggested that resource exclusion is also performed in STEP 3 inaddition to STEP 2.

Note that, in current studies, it is only suggested that the userequipment UE randomly selects one resource that is actually used in datatransmission from the resource subset in STEP 3. That is, as describedabove, in the sensing-based resource selection mode that is proposed incurrent 3GPP, a transmission interval of the D2D signal that istransmitted is not considered. Here, in this embodiment, a partialprocedure is changed on the basis of the procedure of STEP 1 to STEP 3to realize resource selection in consideration of the transmissioninterval of the D2D signal that is transmitted from the user equipmentUE.

<With Regard to Resource Selection Mode According to Embodiment>

Next, description will be given of a sensing-based resource selectionmode that is performed by the user equipment UE according to thisembodiment.

(With Respect to Overview of Sensing-Based Resource Selection Mode)

First, description will be given of an overview of the sensing-basedresource selection mode. The user equipment UE according to thisembodiment has a function of executing the sensing-based resourceselection mode.

In FIG. 10, a subframe n represents a current subframe. “Sensing window”is a time window that is determined in advance in order for the userequipment UE to perform sensing. The user equipment UE performs sensingin a sensing window period to grasp a resource reservation situation inthe future. For example, from a result obtained through sensing in thesensing window, the user equipment UE assumes that D2D control signalstransmitted with resources A2 to A10 illustrated in FIG. 10 is detected.In a case where reservation information indicating reservation ofresources B2 to B10 is included in each of the D2D control signalstransmitted with the resources A2 to A10, the user equipment UE cangrasp a situation in which the resources B2 to B10 among futureresources are reserved already. Note that, a correspondence relationshipbetween the resources in the sensing window and the future resources areexplicitly expressed by the reservation information that is included inthe D2D control signal, or implicitly expressed on the basis ofnotification information (broadcast information), RRC signaling, or acorrespondence relationship (for example, regarding that a resourceafter 1000 ms is reserved, and the like) that is determined in advancein a semi-static manner with standard specifications and the like.

Note that, basically, a length of the sensing window is set to be equalto or longer than the maximum period in which each user equipment thatperforms a communication in this radio communication system can reservea resource of the D2D signal. For example, in a case where the maximumperiod in which the user equipment UE can reserve the resource of theD2D signal is 1000 ms, the length of the sensing period is 1000 ms orlonger. The reason for this is as follows. If the length of the sensingperiod is shorter than the maximum period in which the user equipmentcan reserve the resource of the D2D signal, it is difficult for the userequipment UE, which performs sensing, to appropriately grasp a resourcethat is reserved by another user equipment UE.

“Selection window” is a time window that is determined in advance as aperiod in which the user equipment UE selects a resource among futureresources determined as resources which are not reserved from thesensing result. The user equipment UE performs sensing to grasp areservation situation of the future resources, and selects a resource tobe used for data transmission from resources which are included in theselection window among the grasped resources which are not reserved.

By providing the “selection window”, the user equipment UE operates toselect a resource only in a range of the “selection window” among theresources which are not reserved, and thus latency during datatransmission is shortened. For example, in a case where the “selectionwindow” is set to 100 ms, the user equipment UE selects a resource thatis not reserved within 100 ms. In a case where the “selection window” isnot provided, the user equipment UE selects an arbitrary resource amongresources which are not reserved, and thus data transmission may bedelayed.

Initiation timing and termination timing of the sensing window and theselection window may slide in conformity to the passage of time. Forexample, the initiation timing of the sensing window may be a subframepredetermined subframes before a current subframe, and the terminationtiming may be the current subframe. In addition, the initiation timingof the selection window may be the current subframe, and the terminationtiming may be a subframe predetermine subframes after the currentsubframe. In addition, the initiation timing and the termination timingof the sensing window and the selection window may be boundary timing ofa periodic period (for example, a sidelink control (SC) period) that isconfigured in advance.

(With Respect to Resource Selection Mode According to Embodiment)

Next, description will be given of the sensing-based resource selectionmode in which the user equipment UE according to this embodimentperforms sensing. The user equipment UE according to this embodimentperforms resource selection in consideration of a transmission intervalof the D2D signal that is transmitted from the user equipment UE bychanging a partial procedure among procedures of STEP 1 to STEP 3 whichare described in the column of “<With Respect to Resource Selection ModeThat is studied in 3GPP>”.

[Resource Selection Mode (Mode 1-1)]

In a resource selection mode (mode 1-1), in STEP 3, when performingmeasurement of reception power with a resource with which the D2D signalcan be transmitted, the user equipment UE performs measurement of thereception power in consideration of a desired transmission interval ofthe D2D signal. More specifically, the user equipment UE performs theresource selection in the following procedure. Note that, aconfiguration that is not particularly stated may be the same as in therespective STEPs described in the column of <With Respect to ResourceSelection Mode That is studied in 3GPP>.

STEP 1: Future resources (for example, a future D2D resource pool), withwhich the D2D signal can be transmitted, are regarded as capable ofbeing used (not being reserved).

STEP 2: Among the resources regarded as capable of being used in STEP 1,a resource, which is grasped as a reserved resource through decoding ofD2D control information received in the sensing window, is excluded.Alternatively, among the resources regarded as capable of being used inSTEP 1, a resource, which is grasped as a reserved resource throughdecoding of the D2D control information transmitted from another userequipment UE and satisfies a predetermined condition, is excluded. Forexample, in the example in FIG. 10, among future resources, theresources B1 to B10 are excluded.

STEP 3: Reception power of the entirety of resources (or partialresources which are determined in advance) in the sensing window ismeasured, and the subset of the resources which become the finalresource selection candidate is selected by further excluding futureresources, which are grasped as resources having a correspondencerelationship with partial resources on the basis of the measurementresult, from the remaining resources after exclusion in STEP 2. Next,the user equipment UE randomly selects one resource, which is actuallyused in data transmission, from resources which exist in the selectionwindow in the subset of the resources which become the final resourceselection candidate.

In STEP 3, the user equipment UE detects a resource (unoccupiedresource), which can be selected in the selection window, from thesubset of the resources which become the final resource selectioncandidate, and further excludes the unoccupied resource from the subsetof the resources which become the final resource selection candidate ina case where a measurement result of reception power of a resource onetransmission interval before the unoccupied resource in a past timedirection satisfies a predetermined condition. For example, thepredetermined condition represents a case where the measurement resultof the reception power is equal to or greater than a predeterminedthreshold value. If a plurality of resources (unoccupied resources),which can be selected in the selection window, exist, the sameprocessing is performed with respect to the plurality of unoccupiedresources.

A specific example will be described with reference to FIG. 11 and FIG.12. In FIG. 11 and FIG. 12, resources A2 to A10 are resources with whicha D2D signal is transmitted from another user equipment UE. In addition,it is assumed that resources B2 to B10 having a correspondencerelationship with the resources A2 to A10 are reserved. FIG. 11illustrates a case where a transmission interval, which is desired bythe user equipment UE, of the D2D signal is 100 ms, and FIG. 12illustrates a case where the transmission interval, which is desired bythe user equipment UE, of the D2D signal is 1000 ms.

For example, in FIG. 11, the user equipment UE detects a resource B1 asa resource (unoccupied resource) that can be selected in the selectionwindow. Continuously, the user equipment UE determines whether or not ameasurement result of reception power of the resource A10 that is onetransmission interval before (that is, 100 ms before) the resource B1 isequal to or greater than a predetermined threshold value. In the examplein FIG. 11, in the resource A10, the D2D signal is transmitted fromanother user equipment UE. Accordingly, in a case where a distance fromthe other user equipment UE is short, large reception power to a certainextent is measured. In a case where the measurement result of thereception power of the resource A10 is equal to or greater than apredetermined threshold value, the user equipment UE excludes theresource B1 from the subset of the resources which become the finalresource selection candidate. In this case, the resource B1 is notincluded in the subset of the resources which become the final resourceselection candidate, and thus the user equipment UE selects a resourceother than the resource B1 as a resource that is actually used in datatransmission.

Similarly, in FIG. 12, the user equipment UE detects the resource B1 asa resource (unoccupied resource) that can be selected in the selectionwindow. Continuously, the user equipment UE determines whether or not ameasurement result of reception power of a resource A1 one transmissioninterval before (that is, 1000 ms before) the resource B1 is equal to orgreater than a predetermined threshold value. In the example in FIG. 12,it is assumed that in the resource A1, the D2D signal is not transmittedfrom another user equipment UE, and thus reception power is low (forexample, only noise power, and the like). Accordingly, in the example ofFIG. 12, the user equipment UE does not exclude the resource B1 from thesubset of the resources which become the final resource selectioncandidate. In this case, the resource B1 is also included in the subsetof the resources which become the final resource selection candidate,and thus the resource B1 can be selected as a resource that is actuallyused in data transmission.

[Resource Selection Mode (Mode 1-2)]

Even in a resource selection mode (mode 1-2), in STEP 3, measurement ofreception power is performed in consideration of the transmissioninterval, which is desired by the user equipment UE, of the D2D signalwhen performing measurement of the reception power with a resource withwhich the D2D signal can be transmitted. A configuration that is notparticularly stated is the same as in the resource selection mode (mode1-1). STEP 1 and STEP 2 are the same as in the resource selection mode(mode 1-1), and thus description thereof will be omitted.

STEP 3: Reception power of the entirety of resources (or partialresources which are determined in advance) in the sensing window ismeasured, and future resources, which are grasped as resources having acorrespondence relationship with partial resources on the basis of themeasurement result, are further excluded from the remaining resourcesafter exclusion in STEP 2. According to this, a subset of resourceswhich become a final resource selection candidate is selected.Continuously, the user equipment UE randomly selects one resource, whichis actually used in data transmission, from resources which exist in theselection window in the subset of the resources which become the finalresource selection candidate.

In STEP 3, the user equipment UE detects a resource (unoccupiedresource), which can be selected in the selection window, from thesubset of the resources which become the final resource selectioncandidate, and in a case where a measurement result of reception powerfor a plurality of resources, which are repeated in a transmissioninterval in a past time direction with the unoccupied resource set as astarting point, satisfies a predetermined condition, the unoccupiedresource is further excluded from the subset of the resources whichbecome the final resource selection candidate. Here, for example, theplurality of resources, which become an object to be measured, areresources at the same frequency position determined in a specific timeperiod going back from a resource (the unoccupied resource) that is theresource selection candidate, and resources in the sensing window. Thespecific time period is a single period or a plurality of periods, andmay be determined in advance, may be preconfigured, or may be notifiedby notification information (broadcast information) or higher layersignaling from the base station eNB. The specific time period may be atransmission period (reservation interval) of the user equipment UE thatperforms resource selection. For example, the predetermined condition isa case where an average value of reception power for a plurality ofresources which are repeated in a transmission interval with theunoccupied resource set as a starting point is equal to or greater thana predetermined threshold value. The predetermined condition maycorrespond to a case where the maximum value or the minimum value isequal to or greater than a predetermined threshold value withoutlimitation to the above-described case. In a case where a plurality ofresources (or unoccupied resources), which can be selected in theselection window, exist, the same processing is performed with theplurality of unoccupied resources.

A specific example will be described with reference to FIG. 13 and FIG.14. In FIG. 13 and FIG. 14, resources A2 to A10 are resources with whicha D2D signal is transmitted from another user equipment UE. In addition,it is assumed that resources B2 to B10 having a correspondencerelationship with the resources A2 to A10 are reserved. FIG. 13illustrates a case where a transmission interval, which is desired bythe user equipment UE, of the D2D signal is 100 ms, and FIG. 14illustrates a case where the transmission interval, which is desired bythe user equipment UE, of the D2D signal is 1000 ms. In addition, thepredetermined condition is assumed as a case where an average value ofreception power for a plurality of resources is equal to or greater thana predetermined threshold value.

For example, in FIG. 13, the user equipment UE detects a resource B1 asa resource (unoccupied resource) that can be selected in the selectionwindow. Next, the user equipment UE determines whether or not an averagevalue of measurement results of reception power of the plurality ofresources A1 to A10 which are repeated in a transmission interval withthe resource B1 set as a starting point is equal to or greater than apredetermined threshold value. In the example of FIG. 13, it is assumedthat the D2D signal is transmitted from another user equipment UE in theresources A2 to A10, and thus the average value of the reception poweris large to a certain extent. In a case where the average value of thereception power of the resources A1 to A10 is equal to or greater than apredetermined threshold value, the user equipment UE excludes theresource B1 from the subset of the resources which become the finalresource selection candidate.

Similarly, in FIG. 14, the user equipment UE detects the resource B1 asa resource (unoccupied resource) that can be selected in the selectionwindow. Next, the user equipment UE determines whether or not theaverage value of the measurement values of the reception power of theplurality of resources which are repeated in a transmission intervalwith the resource B1 set as a starting point is equal to or greater thana predetermined threshold value. In the example in FIG. 14, thetransmission interval is 1000 ms, and thus only the resource A1 becomesan object to be determined. In the example of FIG. 14, it is assumedthat the D2D signal is not transmitted from another user equipment UE atthe resource A1, and thus the reception power is low (for example, onlynoise power, and the like). Accordingly, in the example of FIG. 14, theuser equipment UE does not exclude the resource B1 from the subset ofthe resources which become the final resource selection candidate. Inthis case, the resource B1 is also included in the subset of theresources which become the final resource selection candidate, and thusthe resource B1 can be selected as a resource that is actually used indata transmission.

Note that, in the resource selection mode (mode 1-1) and the resourceselection mode (mode 1-2), the transmission interval (resourcereservation period), which can be selected by the user equipment UE, maybe limited. For example, the transmission interval may be limited to aperiod combination in which a relatively great reservation period can bedivided into small reservation periods such as 100 ms, 200 ms, and 1000ms.

For example, it is assumed that the user equipment UE is scheduled totransmit data with a resource X 200 ms after a resource which can beselected in the selection window. In a case where another user equipmentUE, which is scheduled to transmit a signal in a period of 500 ms, isscheduled to transmit data with the resource X, the other user equipmentUE has transmitted a D2D signal with a resource Y 500 ms before theresource X. However, for example, in the resource selection mode (mode1-2), one or a plurality of resources, of which reception power ismeasured in STEP 3 by the user equipment UE, are resources in aninterval of 200 ms, such as a resource 400 ms before the resource X, aresource 600 ms before the resource X, a resource 800 ms before theresource X, which does not include the resource Y. That is, measurementomission occurs. Here, when the transmission interval (resourcereservation period), which can be selected by the user equipment UE, islimited as described above, it is possible to avoid occurrence of themeasurement omission.

Hereinbefore, the resource selection mode (mode 1-1) and the resourceselection mode (1-2) have been described. As illustrated in FIG. 11 andFIG. 13, the resources B2 to B10 are reserved. That is, in a case wherethe transmission interval, which is desired by the user equipment UE, is100 ms, if the user equipment UE performs data transmission by selectingthe resource B1, collision does not occur in first data transmission,but in second or later data transmission (data transmission in theresources B2 to B10), collision occurs. However, according to theresource selection mode (mode 1-1) and the resource selection mode (mode1-2), a resource, for which occurrence of collision is predicted in thesecond or later data transmission, is excluded from the subset of theresources which become the final resource selection candidate, and thusit is possible to suppress occurrence of collision. In addition, in theresource selection mode (mode 1-1) and the resource selection mode (mode1-2), a reservation situation of future resources is determined by usingthe measurement result of the reception power of a resource in thesensing window in addition to decoding result of the D2D controlinformation. According to this, it is possible to further suppressoccurrence of the collision in comparison to a method of determining thereservation situation of the future resources by only the decodingresult of the D2D control information.

In addition, in the resource selection mode (mode 1-2) which isdifferent from the resource selection mode (1-1), in STEP 3, in a casewhere the measurement result of the reception power for the plurality ofresources, which are repeated in a transmission interval from a resource(unoccupied resource) that can be selected in the selection window as astarting point, satisfies a predetermined condition, the unoccupiedresource is excluded from the subset of the resources which become thefinal resource selection candidate. In a case where the D2D signal isnot transmitted from another user equipment UE with the resource A10 inFIG. 11, in the resource selection mode (mode 1-1), the resource B1 isnot excluded from the subset of the resources which become the finalresource selection candidate. On the other hand, in the resourceselection mode (mode 1-2), even in a case where the D2D signal is nottransmitted from other user equipment UE with the resource A10, ameasurement result of reception power of resources (resources A2 to A9)other than the resource A10 is also considered, and thus the resource B1can be excluded from the subset of the resources which become the finalresource selection candidate. That is, the resource selection mode (mode1-2) can further suppress occurrence of collision in comparison to theresource selection mode (mode 1-1).

[Resource Selection Mode (Mode 2)]

In a resource selection mode (mode 2), a new procedure is added betweenSTEP 2 and STEP 3. According to this, a resource, which cannot performdata transmission in a transmission interval desired by the userequipment UE, is excluded from the subset of the resources which becomethe final resource selection candidate in STEP 3. As a result, it ispossible to suppress occurrence of collision.

FIG. 15 is a flowchart illustrating the resource selection mode (mode2). In FIG. 15, “T1” represents a transmission interval desired by theuser equipment UE. “k” represents a positive integral from 1 to K. “K”is a positive integral. “K” may be fixedly determined in advance withstandard specifications and the like, may be preset (preconfigured) inthe user equipment UE by SIM and the like, or may be configured in theuser equipment UE through a base station eNB or a core network.

First, the user equipment UE, which has performed the procedure of STEP1, excludes a resource by using the procedure of STEP 2 (S11). Theprocedure of STEP 1 and STEP 2 is the same as in the resource selectionmode (mode 1-1), and thus description thereof will be omitted.Continuously, the user equipment UE specifies a subset (for convenience,referred to as “second subset” for discrimination from the subset thatis used in STEP 3) of a resource that exists in the selection windowamong resources which are not objects to be excluded in STEP 2, and aplurality of resources k×T1 after the resource as a starting point anddetermined as an object to be excluded in STEP 2 (S12),

A procedure of step S12 will be described in detail with reference toFIG. 16 and FIG. 17. In FIG. 16 and FIG. 17, resource A2 to A10 areresources with which a D2D signal is transmitted from another userequipment UE. In addition, resources B2 to B10 having a correspondencerelationship with the resources A2 to A10 are reserved resources, andare resources determined as being excluded in STEP 2. In addition, inFIG. 16, T1 is set to 100 ms and K is set to 9. In FIG. 17, T1 set to1000 ms and K is set to 1. In a case of FIG. 16, a resource B1 in theselection window, and the resource B2 to the resource B10 after theresource B1 by 100 ms (1×T1) to 900 ms (9×T1) are specified as thesecond subset. On the other hand, in a case of FIG. 17, the secondsubset is not specified.

That is, the resources which are included in the second subset may alsobe referred to as resources which are not suitable as a resource that isactually used in data transmission by the user equipment UE.

Next, the user equipment UE determines whether or not a plurality ofresources (that is, unoccupied resources which are not reserved), whichcan be subjected to repetitive data transmission in a transmissionperiod (T1) desired by the user equipment UE, are included in resourcesafter further excluding the resources of the second subset from theremaining resources after exclusion in step S11 (S13). For example, theuser equipment UE may determine that among resources after furtherexcluding the resources of the second subset from the remainingresources after exclusion in step S11, a resource, which can be used infirst data transmission, is included in the selection window, and aplurality of resources k×T1 after the resource are resources which arenot reserved. In the example of FIG. 16, if K is 9, the user equipmentUE determines whether or not all resources from B1 to B10 areunoccupied. In addition, if K is 2, the user equipment UE determineswhether or not all resources from B1 to B3 are unoccupied. In a case ofYES in step S13, it proceeds to step S14, and in a case of NO in stepS13, it proceeds to step S15.

Next, with regard to the resources which are not objects to be excludedin STEP 2, and are not included in the second subset, the user equipmentUE performs resource selection by using the procedure of STEP 3 (S14).In other words, step S14 may be defined to perform the followingprocedure of STEP 3.

STEP 3: Reception power of the entirety of resources (or partialresources which are determined in advance) in the sensing window ismeasured, and the subset of the resources which become the finalresource selection candidate is selected by further excluding futureresources, which are grasped as resources having a correspondencerelationship with partial resources on the basis of the measurementresult, and the resources of the second subset from the remainingresources after exclusion in STEP 2. Next, the user equipment UErandomly selects one resource, which is actually used in datatransmission, from resources which exist in the selection window in thesubset of the resources which become the final resource selectioncandidate.

Note that, in step 14, the user equipment UE may randomly select oneresource, which is actually used in data transmission, directly fromresources which are not objects to be excluded in STEP 2, are notincluded in the second subset, and exist in the selection window (thatis, the user equipment UE may not perform the resource exclusion that isperformed in STEP 3 on the basis of the measurement result of thereception power). According to this, it is possible to select a resourcethat is used in data transmission from more resources in the selectionwindow.

Next, the user equipment UE selects a resource by using the procedure ofSTEP 3 from resources which are not objects to be excluded in STEP 2 butare included in the second subset (S15). In other words, step S15 may bedefined to perform the following procedure of STEP 3.

STEP 3: Reception power of the entirety of resources (or partialresources which are determined in advance) in the sensing window ismeasured, and the subset of the resources which become the finalresource selection candidate is selected by further excluding futureresources, which are grasped as resources having a correspondencerelationship with partial resources on the basis of the measurementresult, from the remaining resources after exclusion in STEP 2.Continuously, the user equipment UE randomly selects one resource, whichis actually used in data transmission, from resources which exist in theselection window in the subset of the resources which become the finalresource selection candidate. Note that, the user equipment UE mayexecute the procedure of STEP 3 in the resource selection mode (mode1-1) or the resource selection mode (mode 1-2) instead of STEP 3 in stepS15.

Hereinbefore, the resource selection mode (mode 2) has been described.In a case where a plurality of resources, with which repetitive datatransmission can be performed in a transmission period (T1) desired bythe user equipment UE, exist (that is, are not reserved), it proceeds tostep S14. In addition, in step S14, the user equipment UE does notselect the resources (resources which are not suitable as describedabove), which are included in the second subset, as a resource that isactually used in data transmission. That is, one resource, which isactually used in data transmission by the user equipment UE, is aresource with which data transmission is possible also in the subsequenttransmission period, and thus it is possible suppress occurrence ofcollision.

On the other hand, in a case where the plurality of resources, withwhich repetitive data transmission is possible in the transmissionperiod (T1) desired by the user equipment UE, do not exist (that is, arereserved), it proceeds to step S15. In a case of step S15, there is apossibility that the user equipment UE may select the resources includedin the second subset as a resource that is actually used in datatransmission. That is, in the case of step S15, the resource, which isactually used in data transmission by the user equipment UE, is aresource in which possibility of occurrence of collision is high in thesubsequent transmission period. Here, in step S15, the user equipment UEmay give up (stop) data transmission without selecting one resource thatis actually used in data transmission. According to this, it is possibleto suppress occurrence of collision.

In addition, the user equipment UE may execute the procedure in FIG. 15again after passage of predetermined time. According to this, in a casewhere a resource congestion is resolved, data transmission becomespossible.

In addition, in a case of transitioning to step S15, since the userequipment UE regards future transmission resources as being reservedalready by another user equipment UE, resource reservation may not beperformed. According to this, it is possible to avoid transmission ofuseless reservation signaling, and an improvement of space utilizationefficiency of a resource, and an early resource reselection operationare expected.

<Functional Configuration>

(User Equipment)

FIG. 18 is a view illustrating an example of the functionalconfiguration of a user equipment according to an embodiment. Asillustrated in FIG. 18, the user equipment UE includes a signaltransmission unit 101, a signal reception unit 102, a sensing unit 103,and a selection unit 104. Furthermore, FIG. 18 illustrates onlyfunctional units which are particularly related to the embodiment of theinvention in the user equipment UE, and functions (not illustrated) forexecuting at least operations based on LTE are also provided. Inaddition, the functional configuration illustrated in FIG. 18 isillustrative only. A functional classification or the name of thefunctional units may be arbitrarily set as long as the operationaccording to this embodiment can be executed. In addition, a part (onlya partial resource selection sequence, a partial modification example,and the like) of the processing of the user equipment UE as describedabove may be executed.

The signal transmission unit 101 includes a function of creating varioussignals of a physical layer from a D2D signal to be transmitted toanother user equipment UE or the base station eNB, and wirelesslytransmitting the signals. In addition, the signal transmission unit 101includes a transmission function of the D2D signal and a transmissionfunction of a cellular communication. In addition, the signaltransmission unit 101 includes a function of selecting a resource fortransmission of the D2D signal among one or more resource candidatesselected by the selection unit 104, and transmitting the D2D signal.

The signal reception unit 102 includes a function of wirelesslyreceiving various signals from another user equipment UE or the basestation eNB, and acquiring a signal of a further higher layer from asignal of a physical layer which is received. In addition, the signalreception unit 102 includes a reception function of the D2D signal and areception function of the cellular communication.

The sensing unit 103 performs sensing in the sensing window to grasp areservation situation of future resources.

The selection unit 104 includes a function of selecting a resourcecandidate with which the D2D signal can be transmitted on the basis ofthe reservation situation, which is grasped by the sensing unit 103, ofthe future resource. In addition, the selection unit 104 includes afunction of selecting one more resource candidates, with which a signalcan be transmitted, in a selection window subsequent to the sensingwindow on the basis of a sensing result and a transmission interval ofthe D2D signal that is transmitted by the user equipment UE.

In addition, the selection unit 104 may detect an unoccupied resource inthe selection window in accordance with the sensing result, and mayselect one or more resource candidates, with which the D2D signal can betransmitted, by excluding the unoccupied resource from the one or moreresource candidates with which the D2D signal can be transmitted in acase where reception power of a resource one transmission intervalbefore the unoccupied resource in a past time direction is equal to orgreater than a predetermined threshold value.

In addition, the selection unit 104 may detect an unoccupied resource inthe resource selection time window in accordance with the sensingresult, and may select one or more resource candidates, with which theD2D signal can be transmitted, by excluding the unoccupied resource fromone or more resource candidates, with which the D2D signal can betransmitted, in a case where reception power for a plurality ofresources, which are repeated in a transmission interval from theunoccupied resource, as a starting point, in a past time direction,satisfies a predetermined condition. Note that, the case where thepredetermined condition is satisfied may represent a case where amaximum value, an average value, or a minimum value of the receptionpower for the plurality of resources which are repeated in atransmission interval from the unoccupied resource as a starting pointis equal to or greater than a predetermined threshold value.

In addition, the selection unit 104 may detect an unoccupied resource inthe selection window in accordance with the sensing result, and mayexclude the unoccupied resource from one or more resource candidates,with which the D2D signal can be transmitted, in a case where it isdetermined that a plurality of resources, which are repeated in atransmission interval from the unoccupied resource, as a starting point,in a future time direction, are reserved in accordance with the sensingresult.

(Base Station)

FIG. 19 is a view illustrating an example of a functional configurationof the base station according to this embodiment. As illustrated in FIG.19, a base station eNB includes a signal transmission unit 201, a signalreception unit 202, and a notification unit 203. Furthermore, FIG. 19illustrates only functional units which are particularly related to theembodiment of the invention in the base station eNB, and functions (notillustrated) for executing at least operations based on LTE are alsoprovided. In addition, the functional configuration illustrated in FIG.19 is illustrative only. A functional classification or the name of thefunctional units may be arbitrarily set as long as the operationaccording to this embodiment can be executed.

The signal transmission unit 201 includes a function of creating varioussignals of a physical layer from a signal of a higher layer to betransmitted from the base station eNB, and wirelessly transmitting thesignals. The signal reception unit 202 includes a function of wirelesslyreceiving various signals from the user equipment UE, and acquiring asignal of a further higher layer from a signal of a physical layer whichis received.

The notification unit 203 notifies the user equipment UE of variouspieces of information, which are used by the user equipment UE toperform the operations according to this embodiment, by using broadcastinformation (SIB) or RRC signaling. Note that, examples of the variouspieces of information include information indicating configuration of aD2D resource pool, information indicating a position of an SC period,information indicating start timing and end timing of various windows(the sensing window and the selection window), a value of “K”, and thelike.

<Hardware Configuration>

The block diagrams (FIG. 18 and FIG. 19) which are used in descriptionof the embodiment illustrate blocks of a function unit. The functionblocks (constituent units) are realized by an arbitrary combination ofhardware and/or software. In addition, means for realizing respectivefunction blocks is not particularly limited. That is, the respectivefunction blocks may be realized by one device that is physically and/orlogically combined. In addition, two or greater devices, which arephysically and/or logically separated from each other, may be directlyand/or indirectly (for example, wire and/or wirelessly) connected, andthe respective function blocks may be realized by a plurality of thedevices.

For example, the base station eNB and the user equipment UE in theembodiment of the present invention may function as a computer thatexecutes processing of the signal transmission method of the invention.FIG. 20 is a view illustrating an example of a hardware configuration ofthe base station eNB and the user equipment UE according to theembodiment. The base station eNB and the user equipment UE may beconfigured as a computer device that physically includes a processor1001, a memory 1002, a storage 1003, a communication device 1004, aninput device 1005, an output device 1006, a bus 1007, and the like.

Furthermore, in the following description, a term “device” may besubstituted with a circuit, a device, a unit, and the like. The hardwareconfiguration of the base station eNB and the user equipment UE mayinclude the respective devices in the drawing one by one or in a pluralnumber, or may not include a part of the devices.

Respective functions in the base station eNB and the user equipment UEare realized by reading out predetermined software (program) fromhardware such as the processor 1001 and the memory 1002 so as to allowthe processor 1001 to perform an arithmetic operation, and bycontrolling a communication by the communication device 1004, andreading-out and/or input of data in the memory 1002 and the storage1003.

For example, the processor 1001 allows an operating system to operate soas to control the entirety of the computer. The processor 1001 may beconstituted by a central processing unit (CPU) that includes aninterface with a peripheral device, a control device, an arithmeticoperation device, a register, and the like. For example, the signaltransmission unit 201, the signal reception unit 202, and thenotification unit 203 of the base station eNB, and the signaltransmission unit 101, the signal reception unit 102, the sensing unit103, and the selection unit 104 of the user equipment UE may be realizedby the processor 1001.

In addition, the processor 1001 reads out a program (program code), asoftware module, or data from the storage 1003 and/or the communicationdevice 1004 into the memory 1002, and performs various kinds ofprocessing according to the program, the software module, or the data.As the program, a program, which allows the computer to execute at leasta part of the operations described in the embodiment, is used. Forexample, the signal transmission unit 201, the signal reception unit202, and the notification unit 203 of the base station eNB, and thesignal transmission unit 101, the signal reception unit 102, the sensingunit 103, and the selection unit 104 of the user equipment UE may berealized by a control program that is stored in the memory 1002 and isoperated by the processor 1001, and other functional blocks may berealized in the same manner. The above-described various kinds ofprocessing are described to be executed by one processor 1001, but maybe simultaneously or sequentially executed by two or greater processors1001. The processor 1001 may be mounted by one or greater chips. Notethat, the program may be transmitted from a network through electriccommunication line.

The memory 1002 is a computer-readable recording medium, and may beconstituted by, for example, at least one of a read only memory (ROM),an erasable programmable ROM (EPROM), an electrically erasableprogrammable ROM (EEPROM), a random access memory (RAM), and the like.The memory 1002 may be referred to as a register, a cache, a main memory(main storage device), and the like. The memory 1002 can retain aprogram (program code), a software module, and the like which can beexecuted to carry out the signal transmission method according to theembodiment of the invention.

The storage 1003 is a computer-readable recording medium, and may beconstituted by at least one, for example, among an optical disc such asa compact disc ROM (CD-ROM), a hard disk drive, a flexible disk, amagneto-optical disc (for example, a compact disc, a digitalmulti-purpose disc, and a Blue-ray (registered trademark) disc), a smartcard, a flash memory (for example, a card, a stick, a key drive), afloppy (registered trademark) disk, a magnetic strip, and the like. Thestorage 1003 may be referred to as an auxiliary storage device. Forexample, the above-described storage medium may be database includingthe memory 1002 and/or the storage 1003, a server, and other appropriatemedia.

The communication device 1004 is hardware (transmission and receptiondevice) that performs a communication between computers through wireand/or radio network, and may be referred to as, for example, a networkdevice, a network controller, a network card, a communication module,and the like. For example, the signal transmission unit 201 and thesignal reception unit 202 of the base station eNB, and the signaltransmission unit 101 and the signal reception unit 102 of the userequipment UE may be realized by the communication device 1004.

The input device 1005 is an input device (for example, a keyboard, amouse, a microphone, a switch, a button, a sensor, and the like) thatreceives an input from the outside. The output device 1006 is an outputdevice (for example, a display, a speaker, an LED lamp, and the like)that performs output to the outside. Furthermore, the input device 1005and the output device 1006 may have an integral configuration (forexample, a touch panel).

In addition, respective devices including the processor 1001, the memory1002, and the like are connected to each other through a bus 1007 for aninformation communication. The bus 1007 may be configured as a singlebus, or may be configured as a bus that is different between devices.

In addition, the base station eNB and the user equipment UE may includehardware such as a microprocessor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a programmable logicdevice (PLD), and a field programmable gate array (FPGA), or a part orthe entirety of respective function blocks may be realized by thehardware. For example, the processor 1001 may be mounted by at least onepiece of hardware.

<Summary>

As described above, according to the embodiment, there is provided auser equipment that selects a resource for signal transmission on thebasis of a result of sensing that is performed in a sensing time window.The user equipment includes: a selection unit that selects one or moreresource candidates with which a signal is capable of being transmittedin a resource selection time window subsequent to the sensing timewindow on the basis of the sensing result and a transmission interval ofa signal that is transmitted by the user equipment; and a transmissionunit that selects a resource for signal transmission from the one ormore resource candidates which are selected and transmits the signal.According to the user equipment UE, in a mode of selecting a resourcefor signal transmission on the basis of a sensing result, it is possibleto provide a technology capable of suppressing collision of signals.

In addition, the selection unit may detect an unoccupied resource in theresource selection time window in accordance with the sensing result,and may select the one or more resource candidates, with which a signalis capable of being transmitted, by excluding the unoccupied resourcefrom the one or more resource candidates with which a signal is capableof being transmitted in a case where reception power of a resource,which is previous to the unoccupied resource by one transmissioninterval in a past time direction, is equal to or greater than apredetermined threshold value. According to this, a resource in whichoccurrence of collision is predicted in second or later transmission ofthe D2D signal is excluded from resources which become the finalresource selection candidate, and thus it is possible to suppressoccurrence of collision.

In addition, the selection unit may detect an unoccupied resource in theresource selection time window in accordance with the sensing result,and may select the one or more resource candidates, with which a signalis capable of being transmitted, by excluding the unoccupied resourcefrom the one or more resource candidates, with which a signal is capableof being transmitted, in a case where reception power for a plurality ofresources, which are repeated in a transmission interval with theunoccupied resource set as a starting point in a past time direction,satisfies a predetermined condition. According to this, a resource inwhich occurrence of collision is predicted in second or latertransmission of the D2D signal is excluded from resources which becomethe final resource selection candidate, and thus it is possible tofurther suppress occurrence of collision.

In addition, the case where the predetermined condition is satisfied mayrepresent a case where a maximum value, an average value, or a minimumvalue of the reception power for the plurality of resources which arerepeated in a transmission interval with the unoccupied resource set asa starting point is equal to or greater than a predetermined thresholdvalue. According to this, a resource in which occurrence of collision ispredicted in second or later transmission of the D2D signal is excludedfrom resources which become the final resource selection candidate, andthus it is possible to suppress occurrence of collision in variousmethods.

In addition, the selection unit may detect an unoccupied resource in theresource selection time window in accordance with the sensing result,and may exclude the unoccupied resource from the one or more resourcecandidates, with which a signal is capable of being transmitted, in acase where it is determined that a plurality of resources, which arerepeated in a transmission interval with the unoccupied resource set asa starting point in a future time direction, are reserved in accordancewith the sensing result. According to this, one resource, which isactually used in data transmission by the user equipment UE becomes aresource capable of realizing data transmission in the subsequenttransmission period, and thus it is possible to suppress occurrence ofcollision.

In addition, according to the embodiment, there is provided a signaltransmission method that is executed by a user equipment that selects aresource for signal transmission on the basis of a result of sensingperformed in a sensing time window. The method includes: a step ofselecting one or more resource candidates, with which a signal iscapable of being transmitted, in a resource selection time windowsubsequent to the sensing time window on the basis of the sensing resultand a transmission interval of a signal that is transmitted by the userequipment; and a step of selecting a resource for signal transmissionfrom the one or more resource candidates which are selected andtransmitting the signal. According to this signal transmission method,in a mode of selecting a resource for signal transmission on the basisof a sensing result, it is possible to provide a technology capable ofsuppressing collision of signals.

<Supplement of Embodiment>

The D2D control signal may be referred to as scheduling assignment (SA)or an SCI. The PSCCH includes any control channel as long as the controlchannel is a control channel for transmission of control information(SCI and the like) that is used in the D2D communication. The PSSCHincludes any data channel as long as the data channel is a data channelfor transmission of data (MAC PDU and the like) that is used in the D2Dcommunication. The PSDCH includes any data channel as long as the datachannel is a data channel for transmission of data (discovery messageand the like) that is used in the D2D communication of the D2Ddiscovery.

The aspect and the embodiment which are described in this specificationmay also be applied to long term evolution (LTE), LTE-Advanced (LTE-A),SUPER 3G, IMT-Advanced, 4G, 5G, future radio access (FRA), W-CDMA(registered trademark), GSM(registered trademark), CDMA2000, ultramobile broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802.20, ultra-wideband (UWB), Bluetooth (registered trademark), othersystems which use a suitable system, and/or a next generation systemthat is extended on the basis of the systems.

In the procedure, the sequence, the flowchart, and the like in theaspect and the embodiment which are described in this specification, theorder thereof may be changed as long as inconsistency does not occur.For example, with regard to the method that is described in thisspecification, elements of various steps are suggested in an exemplaryorder, and there is no limitation to the specific order that issuggested.

The term “determining” that is used in this specification may includevarious operations. For example, the term “determining” may includeregarding of judging, calculating, computing, processing, deriving,investigating, looking up (for example, looking up in a table, adatabase, or other data structures), or ascertaining as “determined”,and the like. In addition, the “determining” may include regarding ofreceiving (for example, information receiving), transmitting (forexample, information transmitting), input, output, or accessing (forexample, accessing to data in a memory) as “determined”, and the like.In addition, “determining” may include regarding of resolving,selecting, choosing, establishing, comparing, or the like as“determining”. That is, “determining” includes regarding of anyoperation as “determined”.

Description of “on the basis of” in this specification does notrepresent “only on the basis of” unless otherwise stated. In otherwords, description of “on the basis of” represents both “only on thebasis of” and “at least on the basis of”.

In a case where “include”, “including”, and a modification thereof areused in this specification and the appended claims, these terms areintended as comprehensive terms similar to “including (comprising)”. Inaddition, a term (“or”) that is used in this specification and theappended claims is not intended as an exclusive logical sum.

In the entirety of the present disclosure, for example, in a case wherearticles such as “a”, “an”, and “the” are added in translation, thearticles are intended to include a plural form as long as the oppositeintention is not clearly indicated from the context.

The specification discloses the following items.

(Item 1)

A user equipment that selects a resource for signal transmission on thebasis of a result of sensing that is performed in a sensing time window,the user equipment including:

a selection unit that selects one or more resource candidates with whicha signal is capable of being transmitted in a resource selection timewindow subsequent to the sensing time window on the basis of the sensingresult and a transmission interval of a signal that is transmitted bythe user equipment; and

a transmission unit that selects a resource for signal transmission fromthe selected one or more resource candidates and transmits the signal.

(Item 2)

The user equipment according to item 1,

wherein the selection unit detects an unoccupied resource in theresource selection time window in accordance with the sensing result,and selects the one or more resource candidates, with which a signal iscapable of being transmitted, by excluding the unoccupied resource fromthe one or more resource candidates with which a signal is capable ofbeing transmitted in a case where reception power of a resource onetransmission interval before the unoccupied resource in a past timedirection, is equal to or greater than a predetermined threshold value.

(Item 3)

The user equipment according to item 1,

wherein the selection unit detects an unoccupied resource in theresource selection time window in accordance with the sensing result,and selects the one or more resource candidates, with which a signal iscapable of being transmitted, by excluding the unoccupied resource fromthe one or more resource candidates, with which a signal is capable ofbeing transmitted, in a case where reception power of each of aplurality of resources, which are repeated at a transmission intervalwith the unoccupied resource set as a starting point in a past timedirection, satisfies a predetermined condition.

(Item 4)

The user equipment according to item 3,

wherein the case where the predetermined condition is satisfiedrepresents a case where a maximum value, an average value, or a minimumvalue of the reception power of each of the plurality of resources whichare repeated at a transmission interval with the unoccupied resource setas a starting point is equal to or greater than a predeterminedthreshold value.

(Item 5)

The user equipment according to item 1,

wherein the selection unit detects an unoccupied resource in theresource selection time window in accordance with the sensing result,and excludes the unoccupied resource from the one or more resourcecandidates, with which a signal is capable of being transmitted, in acase where it is determined that a plurality of resources, which arerepeated at a transmission interval with the unoccupied resource set asa starting point in a future time direction, are reserved in accordancewith the sensing result.

(Item 6)

A signal transmission method that is executed by a user equipment thatselects a resource for signal transmission on the basis of a result ofsensing performed in a sensing time window, the method including:

a step of selecting one or more resource candidates, with which a signalis capable of being transmitted, in a resource selection time windowsubsequent to the sensing time window on the basis of the sensing resultand a transmission interval of a signal that is transmitted by the userequipment; and

a step of selecting a resource for signal transmission from the selectedone or more resource candidates and transmitting the signal.

Hereinbefore, the invention has been described in detail, but it isapparent by those skilled in the art that the invention is not limitedto the above-described embodiment in this specification. The inventioncan be executed a variation aspect and a modification aspect withoutdeparting from the gist or the scope of the invention which isdetermined by description of the appended claims. Accordingly,description in this specification is made for exemplary explanation, anddoes not have any limiting meaning with respect to the invention.

This patent application claims the benefit of Japanese Priority PatentApplication JP 2016-158269 filed Aug. 10, 2016, and the entire contentsof the Patent Application JP 2016-158269 are incorporated herein byreference.

EXPLANATIONS OF LETTERS OR NUMERALS

UE User equipment

eNB Base station

101 Signal transmission unit

102 Signal reception unit

103 Sensing unit

104 Selection unit

201 Signal transmission unit

202 Signal reception unit

203 Notification unit

1001 Processor

1002 Memory

1003 Storage

1004 Communication device

1005 Input device

1006 Output device

1. A user equipment comprising: a selection unit that selects, based ona result of sensing performed in a first time window and on atransmission interval of a signal, one or more resource candidates in asecond time window after the first time window; and a transmission unitthat selects a resource for transmitting a signal from the selected oneor more resource candidates, and transmits the signal.
 2. The userequipment as claimed in claim 1, wherein the selection unit detects anunoccupied resource in the second time window based on the result ofsensing, and selects the one or more resource candidates by excludingthe unoccupied resource from the one or more resource candidates in acase where reception power of a resource one transmission intervalbefore the unoccupied resource in a past time direction is equal to orgreater than a predetermined threshold value.
 3. The user equipment asclaimed in claim 1, wherein the selection unit detects an unoccupiedresource in the second time window, and excludes the unoccupied resourcefrom the one or more resource candidates based on a predeterminedcondition on reception power of each of a plurality of resources thatare repeated at a transmission interval with the unoccupied resource asa starting point in a past time direction.
 4. The user equipment asclaimed in claim 3, wherein whether the predetermined condition issatisfied or not is determined based on an average value of thereception power of each of a plurality of resources that are repeated ata transmission interval with the unoccupied resource as a startingpoint.
 5. The user equipment as claimed in claim 1, wherein, in a casewhere it is determined, based on the result of sensing, that a pluralityof resources, which are repeated at a transmission interval with aresource in the second time window as a starting point in a future timedirection, are reserved.
 6. A signal transmission method executed by auser equipment comprising: selecting, based on a result of sensingperformed in a first time window and on a transmission interval of asignal, one or more resource candidates in a second time window afterthe first time window; and selecting a resource for transmitting asignal from the selected one or more resource candidates, andtransmitting the signal.